Print lifter and method



y 5, 1938. F. J. SIRCHIE 2,122,589

PRINT LIFTER AND METHOD Filed Aug. 21, 1934 Patented July 5, 1938 YUNITED STATES PATENT OFFICE '4 Claims.

My invention relates to lifters for finger prints and other prints, andto methods of lifting'prints.

A purpose of my invention is to produce a transparent finger printlifter, comprising a trans- 5 parent base sheet, a transparent coatingof adhesive material on the base sheet and a transparent cover sheetover the adhesive material, so that finger prints and similar prints maybe taken up upon the transparent material, and

'10 subsequently protected by the cover sheet, and

may be photographed or inspected by transmitted light passing throughthe lifter.

A further purpose is to provide a transparent base sheet having apermanently plastic adhesive 15 surface for a' finger print lifter.

A further purpose is to produce a finger print lifter having atransparent base sheet with an adhesive coating on the active side and amatte surface on the reverse side, so that writing, with a pencil orsimilar implement, may be applied to the matte surface and will appearin the normally written manner upon a photograph taken toward the activeside by transmitted light through the transparent base. The finger printon the lifter '33 when viewed from the active side is reversed withrespect to the latent finger print, and the photograph of the fingerprint taken from the active side of the base sheet will be unreversed,as will be the photograph of the writing on the matte to surface.

A further purpose is to eliminate photographic highlights by providing amatte surface upon the exposed face of the transparent cover sheet of afinger print lifter.

A further purpose is to improve the composition of the adhesive coatingof a finger print lifter by the use of latex, or of a resin of thepolyhydroxy alcohol-polybasic acid type, with a suitable plasticizer, orof the phenol-formaldehyde type 49 with a suitable plasticizer or of acellulose plastic with a suitable plasticizer.

A further purpose is to employ an adhesive coating on a finger printlifter which is not less than 10 one-thousandths of an inch thick, and

A; not more than 50 one-thousandths of an inch thick.

Further purposes will appear in the specification and in the claims.

In the drawing I have chosen to illustrate but a single embodiment of myinvention, with a minor variation which has proved to be desirable incertain instances.

Figure 1 is a partially broken top plan view of a finger print lifterembodying my invention.

55 Figure 2 is a right side elevation of the finger print lifter ofFigure 1, having the cover sheet partially separated from the base sheetat one corner.

Figure 3 is a top plan view of a powdered finger print. 5

Figure 4 is a top plan view of the same, finger print, to which thefinger print lifter has been applied.

Figure 5 is a front view of the finger print lifter of Figure 4, whichhas been removed from the finger print, has had the cover sheet appliedand has had identifying markings placed upon its reverse side.

Figure 6 is a right side elevation of the finger print lifter of Figure5, with photographic printing paper for making a contact print.

Figure 7 is a variation of Figure 6.

In the drawing like numerals refer to like parts.

The science of finger printing has become so general as an aid to crimedetection, and has so captivated the imagination of the public, that itis deemed unnecessary to dwell upon the use made of finger prints andthe importance of this subject.

It will suffice to say that the contours of the projections anddepressions upon the human cuticle are individual to the particularperson, and that the mere act of touching a surface, even quite lightlyand when the skin is apparently clean, will transfer to that surface thecontours of the cuticle in an oily substance present on the skin.Notwithstanding that the latent finger print thus produced may be whollyinvisible to the naked eye, it has long been known that the latentfinger print may be made visible by powdering it with some substancewhich will adhere at the locations where the oil from the cuticle ispresent, and will not adhere at other locations. After the powder hasbeen applied to the latent print, the excess powder may be removed bybrushing lightly with a camel's hair brush, or by other suitable meanswell known in the art. The result will be as shown in Figure 3, whichillustrates a finger print 20 on a surface 2|, the finger print havingbeen made visible by powdering in a suitable ,45 manner well known inthe art.

The particular powder used has no importance in the present invention.At various times a great many different finger print powders have beenemployed, such as powdered bronze, powdered aluminum, lampblack, chalk,etc. The most successful powders involve mercury, which seems to assistthe powders in adhering to the latent finger print and prevent them fromadhering to other parts of the surface in such manner as tov cause asmear. The product known in pharmacy as mercury with chalk, whichappears by a colloidal suspension of chalk in mercury, or, as analternative, a colloidal suspension of carbon black in mercury, havebeen found by me to be the most efficient finger print powders.

It will be noted, however, that, since the base sheet of my lifter istransparent, and the finger print on the lifter canbe photographed bytransmitted light, it is wholly immaterial whether a black or a whitepowder be used with my lifter, as contrast of color is not ofimportance.

In the prior art, when the latent finger print had been made visible bypowdering, it was normally photographed in place to obtain a perma-'nent record. This necessitated that every finger print expert be askilled photographer, and carry a photographers equipment with him.

As a great many finger prints are usually obtained at the scene of acrime which later prove to be wholly innocent (finger prints ofoccupants of the premises, police ofiicers, etc.) the photographicmethod involved taking and de veloping a great many unnecessary pictureswhich could have been avoided if it were possible to compare the fingerprint with other finger prints without photography.

In cases where the finger print was in a space too small to receive thecamera, or upon a curved surface such as a drinking glass, a gun stock,an automobile steering wheel, etc., it was difficult or impossible toobtain propeixpermanent record by photography.

To avoid these difiiculties, finger print lifters have been devisedwhich normally comprise a sheet of material having a slightly adhesivesur= face, which, when pressed against the powdered latent finger print,will by contact take up some of the powder, but will not stick so firmlyto the surface as to prevent subsequent removal. Thus finger printlifters have been made from photograph film, from which the silver hadbeen removed by a solution of sodium thiosulphate prior to use.Likewise, rubber sheeting similar to that used for automobile tirepatches has been employed for finger print lifters. This sheeting formedthe base sheet, and a cover sheet of linen or similar material was usedto prevent the rubber surface from losing its tackiness before it wasemployed.

In some cases the cover sheet was of transparent material. This had theadvantage that the cover could be replaced after the finger print hadbeen lifted, and the finger print could be photographed by reflectedlight through the cover sheet.

I have discovered that a vastly superior finger print lifter may beproduced by using a transparent base sheet and transparent adhesive orpermanently tacky material on the base sheet, with a transparent coversheet. I illustrate in Figure 1 a base sheet 22 formed of any suitabletransparent sheet material which is sufficiently pliable for'this use. Ihave found celluloid, cellulose acetate or thick cellophane (liberatedcellulose) to be desirable materials for the base sheet. The thicknessof the base sheet should be 2 to one-thousandths of an inch, preferably5 one-thousandths of an inch. The base sheet 22 has on its active sideor face a coating 23 of adhesive or permanently tacky material, which issuificiently adhesive to pick up the powder of the powdered fingerprint, but not surficiently adhesive to adhere firmly to the surfaceupon which the finger print is found. The adhesive material ispreferably light in color but it need not necessarily be light in colorprovided it is transparent. There are of course various degrees oftransparency, but it is suflicient that the lifter pass transmittedlight which is strong enough to produce a photograph. When I refer tothe lifter as transparent, I mean to include also the conditionsometimes known in other arts as translucent, provided sufilcient lightcan pass through the lifter to take a photograph or to permit inspectionby transmitted light. The degree of stickiness of the adhesive coatingmay vary considerably with the material used and with the age of theparticular finger print lifter, but it should not change so much thatthe adhesive material becomes at anytime very sticky (as in hot weather)or very nonadhesive.

It will be understood that my finger print lifter will be used uponoccasion to lift other prints, such as palm prints, foot prints, etc.,and also to lift writing and signatures. For the latter use no powder isemployed, the ink or other writing material adhering slightly to theadhesive material of the lifter. The adhesive quality of the'adhesivematerial may vary somewhat to suit these special uses.

I have in mind a wide selection of adhesive materials which may be used.Attempts have been made in the past to apply a solvent to the base sheetand use the softened surface of the base sheet as an adhesive surface,but this has not been found to be very satisfactory. One adhesivematerial which I have used with some success is gelatin. I have in somecases mixed the gelatin with glue, and in other cases with sugar. Inmostinstances I find that the glue or sugar, where used, should not bemore than of the weight of the gelatin. The amount of water added todissolve the gelatin at the time that the gelatin is applied is a matterof discretion and depends upon the thickness of film to be produced.Equal parts of gelatin and water are usually satisfactory. Gelatin hasthe disadvantage that it melts when subjected to considerable heatduring photographing.

I have found that coagulated latex makes a quite satisfactory adhesivematerial to be applied to the active side of the base sheet. Coagulationmay be produced merely by evaporation of the continuous phase.

A desirable adhesive material maybe made from resins of the polyhydroxyalcohol-polybasic acid type, such as glycerol-phthalic acid resin, towhich suitable plasticizers have been added. Of the plasticizers whichare satisfactory, I suggest vegetable oils, such as castor oil, mineraloils, and fatty acids such as stearic acid, oleic acid and palmiticacid. The quantities of plasticizers to be used will depend, of course,upon the particular plasticizer. but suflicient plasticizer should beadded to make the resin permanently plastic, so that it will remainplastic even after a period of many months.

Resins of the phenol-formaldehyde type, with proper plasticizers, mayalso be used for the adhesive material.

The most desirable adhesive material, of which I know, is made fromcellulose nitrate (pyroxylin) with a suitable plasticizer. Theplacticizer may comprise a vegetable oil such as castor oil, or dibutylphthalate or diethyl phthalate or butyl tartarate or triacetin, or anywell known pyroxylin plasticizer.

A specific composition which has been found very successful comprisesten parts by weight of pyroxylin, thirty parts by weight of castor oil,and one part by weight'of tricresol phosphate, diluted to sprayingconsistency by a suitable solvent. The solvent which I have found mostsuccessful comprises by weight 65% of toluol, 15% of butyl alcohol, 10%of methyl-ethyl-ketone, 5% of ethylene-glycol-mono-ethyl ether and 5% ofthe acetate of ethylene-glycol-monoethyl ether. It will be understood,-of course, that a wide variety of other solvents may be suggested by anyplastic chemist.

The polyhydroxy alcohol-polybasic acid type, phenol-formaldehyde typeand cellulose nitrate type adhesives are specifically the invention ofLawrence R. Dallett.

Whatever adhesive material is used, I will apply a cover sheet 24 to theadhesive coating as soon as the adhesive coating has been spread acrossthe base material, the cover sheet 24 assisting in preventing theadhesive coating from drying by excluding the air at all points exceptthe edges. As explained above, where I am employing an adhesive materialwhich has a tendency to become permanently dry and nonadhesive, I willprevent this by suitable plasticizers, as explained. From the standpointof the plastic chemist, the plastic used in my adhesive material, wherea plastic is employed, will be overplasticized.

As a result of a careful study of the film thickness of the adhesivecoating, I have discovered that adhesive coatings which would otherwisebe satisfactory may fail because of their excessive thinness. Thesurface upon which the finger print is placed almost invariably hasminute irregularities to which the finger producing the finger printmore or less conforms when it is pressed against the surface. If thefinger print lifter is to pick up the finger print perfectly, theadhesive surface must also conform to these irregularities. In the past,where the base sheet of the lifter was rubber, the base sheet wascapable of conforming to irregularities in the surface regardless of thethickness of the adhesive coating, provided sufficient pressure wasapplied. Unfortunately, however, the rubber is resilient besides beingpliable, and, where it is supported by two projections from the surfacecontaining the finger print, the rubber will extend directly across fromone projection to another, due to its resilience, rather than bend downinto the depression between the projections, unless extreme care betaken to apply pressure to the rubber exactly back of the depression. Ithas therefore resulted, as a practical matter, that the prior artlifters would faithfully reproduce the finger print on the projectionsof the surface but would miss the detail or miss altogether the portionof the finger print in minute depressions of the surface.

I have discovered that this difficulty may be corrected by substantiallyincreasing the thickness of the adhesive coating 23, so that, when thelifter is applied to the surface, the minute projections on the surfacewill penetrate the adhesive coating and the adhesive coating will beforced into the minute depressions. As a result, the adhesive coatingwhich carriesthe lifted finger print may have a few thousandths of aninch variation in thickness where it has been rendered thinner by aprojection or rendered thicker by a depression into which it is forced,but the adhesive material will faithfully pick up the finger print bothon the projections and in the depressions of the surface.

I have discovered that the adhesive coating 23 should be at leastone-thousandths of an inch thick, and preferably one-thousandths, of aninch thick. The upper limit of thickness of the adhesive material ismuch less important than the lower limit of thickness, but I find thatobjectionable distortion during photography is produced where theadhesive coating 23 is thicker than 50 one-thousandths of an inch.

To obtain a uniform coating of the desired thickness, let us say 20one-thousandths of an inch, I find that the most convenient way is tospray the adhesive material upon the active side of the base sheet 22.The adhesive coating may desirably be applied to a large sheet, which,after doubling with a large cover sheet, can be cut into a great numberof pieces each of suitable size for a single lifter. Where spraying isaccomplished at a uniform rate, a layer of a fewone thousandths of aninch may be deposited each time the spray passes over the sheet, and thethickness of the adhesive coating may be accurately determined by thenumber of times that the spraying is repeated. The adhesive coating mayalso be distributed by a roll, running the base sheet under a knife edgeto remove any excess thickness.

It will be understood that the manner of application of the adhesivematerial is not of vital importance in the present invention, providingthe adhesive material is firmly attached to the base sheet, thedistribution is reasonably uniform and the desired film thickness isobtained.

Where irregularities on the surface cannot be cared for by the thicknessof the adhesive coating, it will of course be evident that the basesheet 22, which will preferably comprise one of the cellulose nitrate,cellulose acetate or cellulose, transparent pliable materials, can byits pliable nature conform to the irregularities of the surface.

When preparing to use my novel lifter, I will first powder the fingerprint, palm print; foot print, etc., as in the prior art. Where writingis to be lifted, no powdering is used. I will then remove the coversheet 24, preferably by turning up one comer "with the finger nail, andplace the cover sheet aside for further use. I will then apply the basesheet 22 to the powdered finger print with the adhesive coating 23directly against the finger print. This is shown in Figure 4, where thefinger print 20 is covered by the base sheet 22, the active face 25 ofthe base sheet being toward the print. With the base sheet and adhesivematerial in the position of Figure 4, the lifter will be pressed firmlyagainst the surface 2| desirably by running the finger over the rearside 21 of the lifter, applying gentle pressure to the lifter.

The base sheet and adhesive coating are then removed from the surface2|, using care to lift the adhesive coating away from the surface andnot slide the adhesive coating along the surface in such manner as tosmear the print. As soon as the base sheet 22 and adhesive coating 23are removed from the surface 2| with the lifted finger print, the coversheet 24 is carefully replaced, preferably returning the surface 28which was formerly in contact with the adhesive coating, to its formerposition against the adhesive coating. The lifter is then as shown inFigure 5 where the cover sheet face 29 is uppermost.

The finger print may now be studied in detail by the technician, whowill preferably observe it from the rear side 21 of the base sheet. Theprint as seen from the side 29 of the cover sheet i reversed withrespect to the print 20 on the surface 2 I. By analogy to photography,the print of Figure 3 is the image, the print as seen in Figure 5, fromthe side 29 of the cover sheet (or from the active side 25 of the basesheet) is a negative (from the standpoint of its being right side left,not of color), and the print as seen in Figure 4 from the rear side 21of the base sheetis the positive (from the standpoint of its being rightside right). The technician may observe the finger print as a positiveby looking at the rear side 21 of the base sheet, without the necessityof photographing the finger print to change it to a positive.

On the other hand, where a permanent photographic record is desired, thephotograph should be taken from the side 29 of the cover sheet (thenegative side of the lifter), so that the photograph obtained will be apositive. In obtaining a photograph of the lifted finger print, it isnot necessary to use a camera, as the photographic printing paper 30 maymerely be placed against the side 29 of the cover sheet, as shown inFigure 6, making a contact print. Whether a contact print is made, or aphotograph is made by means of a camera, I refer to the photographicreproduction as a photograph. Where an enlargement is to be taken in onestep, the photograph should also be taken from the side 29 of the coversheet, so that the enlargement will be a positive.

As most of the finger prints obtained are intended for use as evidence,it is highly important that the finger prints be identified in a mannerwhich cannot be criticized by opposing counsel. The identificationmarkings should preferably appear as part of the permanent photographicrecord. This can readily be accomplished by my invention. I preferablyemploy a base sheet whose rear side 2'! has a matte or frosted surface.This gives a gray background against which the finger print may beobserved from the side 29 of the cover sheet, regardless of whetherlight or dark colored powder is used. If the cover sheet 24 is notprovided with a matte surface, the matte surface upon the base sheetaids in distinguishing the base sheet from the cover sheet. The mattesurface on the base sheet also eliminates highlights in photography andreduces the transmitted light intensity sumciently to permit the makingof contact prints from standard printing papers without a camera, andwithout danger of over-exposure. The matte surface also will receivewriting very acceptably, especially from a pencil. In Figure 5 I showwriting 3| upon the rear side 21 of the base sheet, which side has amatte surface. When viewed from the side 29 of the cover sheet, thewriting 3| is reversed, but this agrees with the position of the fingerprint, which is a negative when viewed from that side. When a photographis obtained from the side 29, it will be a positive, both 'in respect tothe finger print and to the writing.

It may in some instances be desirable to "employ a matte surface on theside 29 of the cover sheet 24 (Figure 7) to avoid highlights inphotography, when photographing from that side, in case a matte surfaceis not to be used on the base sheet.

Where the latent finger print is to be com- "placing the lifter in theenlarging frame.

The base and cover sheets may desirably have a thickness of about 5one-thousandths of an inch. It will be understood also that advantagemay be obtained from any one of the enumerated features of my invention,without necessarily using the others, although the most desirable formof my invention will employ all of the advantageous features.

In view of my invention and disclosure variations and modifications tomeet individual whim or particular need will doubtless become evident toothers skilled in the art, to obtain all or part.

of the benefits of my invention without copying the structure shown, andI, therefore, claim all such in so far as they fall within thereasonable spirit and scope of my invention.

Having thus described my invention, what I claim as new and desire tosecure by Letters Patent is:

1. The method of obtaining a permanent record of a latent finger print,which consists in powdering the finger print, in applying pliabletransparent-material having a transparent adhesive face to the fingerprint, in removing said material to lift the finger print, in applyingpliable transparent covering material to the adhesive face, in placingwriting on such part of the material as will make the writing visible asa positive on the side on which the lifted finger print is visible as apositive and visible as a negative on the side on which the liftedfinger print is visible as a negative, and in making a photograph of thelifted finger print and the writing.

2. The method of obtaining a permanent record of a latent finger print,which consists in rendering the latent finger print transferable bycontact, in bringing an adhesive surface of pliable transparent materialinto contact with the finger print, in removing the pliable transparentmaterial from the finger print and thus lifting the finger print, inapplying writing to the opposite side from the adhesive side of thepliable transparent material and in making a photo-.

i. transparent base sheet, a coating of adhesive material on one side ofthe base sheet, and a cover sheet of pliable transparent material uponthe adhesive coating, said cover sheet having a matte surface upon theside away from the adhesive material.

FRANCIS J. SIRCHIE.

